v.exe: clone the repo on first launch

compiler/main.v

@@ -782,7 +782,15 @@ fn new_v(args[]string) *V {
 			println('Setting VROOT to "$lang_dir".')
 			os.write_file(TmpPath + '/VROOT', lang_dir)
 		} else {
-			println('Please do it from "v/compiler" directory.')
+			println('V repo not found. Cloning...') 
+			os.mv('v', 'v.bin') 
+			os.system('git clone https://github.com/vlang/v') 
+			if !os.dir_exists('v') {
+				println('failed to clone github.com/vlang/v') 
+				exit(1) 
+			} 
+			os.mv('v.bin', 'v/compiler/v') 
+			println('Re-launch V from v/compiler') 
 			exit(1) 
 		}
 	} 

os/os.v

@@ -84,6 +84,10 @@ pub fn file_size(path string) int {
 	return 0
 }
 
+pub fn mv(old, new string) {
+	C.rename(old.cstr(), new.cstr()) 
+} 
+
 pub fn file_last_mod_unix(path string) int {
 	# struct stat attr;
 	# stat(path.str, &attr);